The device relates to a device for heat treatment of permeable webs of goods, especially textiles such as fabrics, warp knits, tissues, fleeces, and the like, with a housing in which at least one screen roller is mounted and a pumping device is associated endwise with the screen roller, said pumping device drawing a processing medium in the form of a vapor and/or gas out of the screen roller. The through-flow area, in other words the working width of the screen roller, can be determined by a width-adjusting device at the screen roller and a screen lid or a fixed cylindrical body in the form of a screen are located externally relative to the screen roller to even out the flow.
A device of this kind is shown in DE-A 19 00 496. In that document, the screen lid for evening out the through air flow over the length of the screen roller is also disclosed. Normally the screen lid is permeable to air over the entire length of the screen roller, but in this case this is only true in the middle area because a working width adjustment is provided in the middle of the roller. For this purpose, the screen roller surrounds an additional wall that extends up to the screen lid. The wall is axially adjustable by several spindles located around the roller. In order to avoid "false air" --in other words, air that does not flow through the web of goods to be processed but instead flows directly through the uncovered roller area straight to the fan--with a small working width setting, the screen lid is therefore permeable to air only in the middle area. A width-adjusting device of this kind is very costly, if only because of the many drive spindles that must be provided around the roller. In addition, this design is less suitable for wide webs of goods because the processing air for the marginal areas of the web must flow from the middle of the screen lid, which is the only permeable part, to these marginal areas. It is not possible to expose the screen roller uniformly to processing air over the width of the web of goods.
The design according to DE-A 19 26 742 is advantageous in this regard. In that document, a screen roller is disclosed that consists of two axially arranged screen roller jackets mounted with a distance between them. This design has the advantage that the second, inner screen roller jacket can be used as an additional blocking element. This is particularly true if the permeability of the inner jacket to air is less than that of the outer screen roller jacket. In this document, an outer screen lid is also disclosed so that the air entering from a fan is initially blocked at this lid over the length of the roller, and is therefore evened out. Then it flows uniformly over any working width through the goods on the roller and is blocked again by the second inner jacket, which not only permits more uniform processing over the working width but even makes a mechanical width adjustment superfluous because the permeability of the roller is reduced overall. However, this is effective only in the area of the roller that is free of the web since the textile itself generally offers a greater resistance to the passage of the air than the double jacket. In order to avoid "false air" --air flowing axially between the jackets--here as well, fixed panels are provided in the outer area of the roller and extend radially between the jackets around the roller.
The solution according to DE-A 19 26 742, without a mechanical width adjustment, is viewed as a compromise. Especially for larger working widths, and therefore long screen rollers, and larger different working widths, this design is not satisfactory in terms of its drying ability.